Search

Enteropathogenic Escherichia coli (EPEC) secretes many Esps (E. coli-secreted proteins) and effectors via the type III secretion (TTS) system. We previously identified a novel needle complex (NC) composed of a basal body and a needle structure containing an expandable EspA sheath-like structure as a central part of the EPEC TTS apparatus. To further investigate the structure and protein components of the EPEC NC, we purified it in successive centrifugal steps. Finally, NCs with long EspA sheath-like structures could be separated from those with short needle structures on the basis of their densities. Although the highly purified NC appeared to lack an inner ring in the basal body, its core structure, composed of an outer ring and a central rod, was observed by transmission electron microscopy. Matrix-assisted laser desorption ionization-time-of-flight mass spectrometry, Western blot, and immunoelectron microscopic analyses revealed that EscC was a major protein component of the outer ring in the core basal body. To investigate the mechanisms of assembly of the basal body, interactions between the presumed components of the EPEC TTS apparatus were analyzed by a glutathione S-transferase pulldown assay. The EscC outer ring protein was associated with both the EscF needle protein and EscD, a presumed inner membrane protein. EscF was also associated with Esc J, a presumed inner ring protein. Furthermore, escC, escD, and escJ mutant strains were unable to produce the TTS apparatus, and thereby the secretion of the Esp proteins and Tir effector was abolished. These results indicate that EscC, EscD, and EscJ are required for the formation of the TTS apparatus.

The cytotoxicity of Bordetella bronchiseptica to infected cells is known to be dependent on a B. bronchiseptica type III secretion system. Although BopB, BopN, BopD, and Bsp22 have been identified as type III secreted proteins, these proteins remain to be characterized. In this study, in order to clarify the function of BopD during Bordetella infection, a BopD mutant was generated. Although secretion of BopD into the culture supernatant was completely abolished by the bopD mutation, the secretion of other type III secreted proteins was not affected by this mutation. It has been reported that severe cytotoxicity, including cell detachment from the substrata, and release of lactate dehydrogenase (LDH) into the supernatant are induced in L2 cells by wild-type B. bronchiseptica infection, and these phenotypes are dependent on the type III secretion system. In contrast, neither cell detachment nor LDH release was induced in L2 cells infected with the BopD mutant. Furthermore, the hemolytic activity of the BopD mutant was greatly impaired compared with that of the wild-type strain. On the basis of the results of coimmunoprecipitation assays with anti-BopB antibodies, we conclude that BopD has the ability to associate with BopB. Finally, we show that the BopD-BopB complex is responsible for the pore formation in the host plasma membrane that functions as the conduit for the transition of effector proteins into host cells.

DNA hybridization studies and Western blot analysis reveal that plasmid pNL2001 of Salmonella enteritidis contains Spv region and the Spv gene is involved in the expression of virulence of S. enteritidis. The amino acid sequences of the four Spv proteins of Salmonella species reveal close resemblance to the corresponding sequences in the virulence region of their plasmids.

The Luzon Earthquake of 1990 (M(sub s) = 7.8) caused soil liquefaction in a widespread area that in turn caused crucial damage to various structures. After presenting an overview of the geotechnical aspects of the earthquake, this paper describes damage patterns of buildings in Dagupan City where fine to silty sands liquefied extensively. Also presented are geomorphological conditions, Standard Penetration Test (SPT) results, and shear wave velocity (V(sub s)) profiles determined by a Rayleigh wave method; and their relations to the building damage of the city. The buildings that suffered large settlement and tilting are found to be concentrated in the banks of active rivers and in the fills built on recently abandoned river channels. It is found that the currently available empirical correlations using SPT N-value can well estimate the extent of liquefaction-induced damage to buildings. The Rayleigh wave method used shows capability in determining cross sections of V(sub s) structure in the near surface soil.